Oil burner control thermomagnetic switch



April 2, 1940. H. c. ROHR 2,195,633

I OIL BURNER CONTROL THERMOMAGNETIC SWITCH Filed July 27, 1936 M 4 u/ve 2 6 LmZul R0 OM T/IERMOS 74 T I PERM/44f? MAG/VET 7 1 Patented Apr- 2, 1940 UNITED STATES PATENT OFFICE This invention relates to control systems and eral Motors Corporation, Detroit, Micln, a corporation of Delaware Application July 27, 1936, Serial No. 92,841

7 Claims. (Cl. 158-28) to ignite the fuel. Connected in series with the more specifically to controlling systems for use with means for supplying heat to a desired area such as fluid fuel furnaces,

5 With the. widespread use of fiuid fuel furnaces, such as for example, oil burners, it has become necessary to design for the control thereof, an apparatus which will keep within desired limits the temperature within a given space to be heatl ed by controlling the operation of combustion means, which means is usually a motor which supplies both fuel and air to a cumbustion space.

These systems also of necessity must include certain safety factors which assume control of the 16 system in case of abnormal operation thereof.

Certain of the abnormal conditions which must be accommodated are first, the failure of the burner to start initially upon a call for heat from the heated area. Second, a failure of the flame a at any time during normal operation thereof, and third, failure of a current when the burner is operating normally otherwise it is only necessary to have the burner energized at such periods as there is a desire for heat within the heated 1 area, and to turn oil the burner at such time as when the heat supply is sufilcient.

It is, therefore, the object of my invention to provide a system for controlling .a fiuid fuel burner which will fulfill the necessary safety requirements outlined above and will be rugged and practical in operation.

With this and other objects in view which will become apparent as the specification proceeds, my invention resides in the construction as set forth in the following specification and claims and illustrated in the accompanying drawing, in which the figure is a schematic wiring diagram of the construction of a control system according to my invention.

0 Any suitable supply line I and l is provided which may be connected to any desired source of electricity. Directly connected across this line is the primary I of a transformer 8 for supplying current by means of its secondary II to the low voltage control circuit of the system. Directly connectedacrossthelughtensionlinebylines II, II and ilisamotorinonnallyutiliaedtosupplyfueltothecombustionspace. Insertedbetween lines it and It is a pair of contacts II and 5 22 which operate as a main motor switch to energise and deenerglse the motor. Connected directlyacrossbetweenlines "and ltistheprimary 20 of an ignition transformer, the secondary I. having connected thereacross an ignition sparkgapflaerosswhiehsparksaredischarged primary 24 is a mercury switch II which is operated by a bimetallic stack element to deenergise the primary it under certain conditions which will be disclosed at a later point. I

The remainder of the circuit operates on a low or reduced voltage from the transformer secondary II and includes a room thermostat 32 having contacts 34 and 30, an additional switch also operated from the bimetallic stack element as explained-in relation to switch It, the two being normally positioned together but here shown spaced apart for clarity, a relay pull or energizing coil ll attracting an armature 42, said armature having thereon the main motor contact 2! which 16 cooperates with the stationary contact and in addition contact 43 which cooperates with they stationary contact I to provide a circuit through a hold coil II to maintain the armature in the raised position as will later be explained, the two so sets of contacts being insulated from each other.

As a safety feature there is also provided a permanent magnet ll having an armature II, said armature carrying a movable contact 52 cooperating with a stationary contact 54 and providing 15 therewith a safety switch. The particular construction of the armature ll of the permanent magnet II is such that as the temperature thereof increases the magnetic properties of attraction of the armature and the magnet decreases so that so upon a certain temperature rise the permanent magnet may no longer hold the armature in its raised position and it therefore falls opening contacts "-44. The heat for operating the switch in this manner is provided by the pull coil ll of 35 the relay. said coil ll having only a thermo-connection to the armature SI and no eifective masnetic connection exists therebetween the heat from the coil effecting a change in the temperature of the magnet due to its proximity thereto.

Under normal conditions with the apparatus at rest and the temperature in a space to be heated at a sufficiently high point, contacts "-38 are opened, switch "is closed, switch 30 is closed and contacts 52- are closed. The motor switch 2l22 is opened and the holding circuit is open at 43-44. With this condition existing, as the room thermostat calls for heat, contacts u-Jt close which causes the following circuit through the pull coil 40 from secondary ll: line 50, room thermostat 32, contacts "-36, line II, contacts "-44, line 6|, switch 38, line", pull coil 4., line '4, line I. When coil ll is thus en-' ergized, it attracts its armature l! which closu the motor switch "-22 thereby energizing the u motor and it begins to discharge fuel into the combustion chamber. At the same time current also flows through the ignition transformer by an obvious circuit therefore providing ignition and the fuel is therefore ignited by the discharge of electric sparks and the burner is started in operation.

Simultaneously, with the closing of the motor switch 20-22, the attraction of armature 42 causes the contacts 43-44 to close which causes the following circuit through hold coil 46: secondary Ill, line i, line 68, contacts 43-44, hold coil 48, line 10, contacts 5452, line 58, contacts 3-34 and line 56 back to the secondary Hi. This hold coil 46 is capable of maintaining armature 42 in its raised position and contacts 4344 closed. Therefore, in normal conditions, the

temperature in the combustion chamber rises, the bi-metallic stack thermostat rotates to open the ignition switch 30 therefore cutting off the ignition of the burner and also to open switch 38 for deenergizing pull coil 40 and therefore prevents the heat from the same from causing the switch contacts 52-54 to open. At this time, however, the hold coil 48 maintains the necessary contacts such as before mentioned. The burner therefore operates normally under these condi tions until the supply of heat to the desired space is satisfied whereupon the room thermostat opens contacts 34-36 and the whole system is again deenergized.

If, however, for some reason the burner does not initially ignite as it should, the stack thermostat does not open and heat coil 40 remains in circuit providing heat to the armature 50 of the permanent magnet 48. After a predeter 'for some reason or other the flame is extinguished due to presence of air or water in the oil, the stack thermostat will begin to cool down and will eventually close switch 38 reinserting coil 44 in the circuit and the heat therefrom will again heat the armature II to cause the warp switch 82-44 to open. If under normal operating conditions, with the burner proceeding as usual, there is a current failure, the hold coil 46 will be deenergized to drop its armature 42 therefore deenergizing the high voltage circuit and also its own holding circuit through contacts 4344, the armature 42 can then not again be attracted until the switch 38 operated by the stack thermostat is closed to allow the energization of coil 4| which causes a delay and allows the furnace to be purged of any explosive fuels i which might cause a dangerous explosion if the furnace was allowed to come on immediately following a current failure.

It will be noted that this system is one in I which the ignition is out off after the burner is started or what is called intermittent ignition. The may be made a constant ignition system by merely eliminating the switch from the circuit which will place the transformer 24 directly across the motor and the ignition will be on whenever the motor is running.

It is, therefore, obvious that I have provided a simple, efllcient and practical construction for operating oil burners or like fluid fuel burners which will function satisfactorily and operate the burner throughout any abnormal conditions in perfect safety.

I claim:

1. In a control system for fuel burners, in circuit, means for propelling fuel into a combustion space, a elay for controlling the operation of the means, a safety switch dominating relay operation, magnetic means for maintaining the safety switch in closed position, said magnetic means being in juxtaposition to the relay whereby the heat generated by the relay will effect the magnetic properties of the safety switch and cause it to open after a predetermined time.

2. In a control system for fuel burners, in circuit, means for propelling fuel into a combustion space, a relay controlling the operation of the propelling means, said relay having a pull coil and a hold coil, means for energizing the pull coil to initially close the relay to energize the propelling means, means for energizing the hold coil to maintain the relay closed, a safety switch normally closed, magnetic means to maintain said safety switch closed located in juxtaposition to the pull coil whereby the heat generated in the pull coil will cause a change in the magnetic characteristics and the safety switch will open after the pull coil has remained energized for a certain length of time and means responsive to combustion conditions within the burner to deenergize the pull coil upon a temperature rise in the burner and thus prevent operation of the safety switch.

3. In a control system for fuel burners, in circuit, a motor for supplying fuel to a combustion space, ignition means for igniting the fuel, a relay comprising a pull coil, a hold coil and an armature, a plurality of switches operated by the armature, said switches controlling the motor and ignition and the energization of the hold coil and a safety switch magnetically maintained closed in juxtaposition to the pull coil whereby the heating effect of the pull coil changes the magnetic characteristics of the safety switch to open the same after a predetermined heating period by the pull coil.

4. In a control system for fuel burners, in circuit, a motor for supplying fuel to a combustion space, a switch controlling motor operation, a safety switch and a single means effecting operation of the motor switch and the safety switch due to two different physical effects thereof.

5. In a control system for fuel burners, a high and a low voltage circuit, a motor, motor switch and ignition means in the hi h voltage circuit, a safety switch and motor switc operating means in the low voltage circuit, permanent magnet means for normally holding the safety switch closed in juxtaposition to the switch operating means whereby when the switch operating means is energized to magnetically operate the motor switch the heat generated by the coil causes a change in the magnetic characteristics of the safety switch holding magnet and if allowed to heat for a sufficient period will cause the safety switch to drop out.

6. In a control system for fuel burners, a high and a low voltage circuit, a motor, motor switch and ignition means in the high voltage circuit, a plurality of thermally o erated switches, a safety switch and a plurality of coils in the low voltage circuit, magnetic holding means for maintaining the safety switch normally closed, one of said coils closing said motor switch and one maintaining it closed, said magnetic holding means being in proximity to the closing coil and affected by the heat generated thereby, one of said thermal switches controlling the circuit through the closing coil and the other thermal switch controlling the energizing periods of the whole system.

7. In a control circuit, a relay including a pull coil and a hold coil. an armature actuated by the coilsfor controllingthecircuit,asafety switch in juxtaposition to one of the coils, a, magnet for maintaining the safety switch closed havingcharacteristics such that its attractive strength decreases upon an increase in the heat of the magnet and its juxtaposition being such that one oi the coils will heat the magnet if current is flowing therethroush.

HENRY 0.11.0113. 

